System and method for enhancing compression using skip macro block on a compressed video

ABSTRACT

A method, apparatus and a computer readable medium for skipping macro blocks of a compressed video. The method includes, for at least one INTER frame, saving a set of macro blocks including at least one of a macro block having a motion vector greater than a predetermined motion vector threshold, a macro block having positional correspondence to at least one macro block having a motion vector, a macro block having a size greater than a predetermined macro block size threshold, and a macro block having positional correspondence to a second macro block in a previous group of pictures, the second macro block having a motion vector. The method deletes and marks as skipped one or more remaining macro blocks, and merges the set in an order to create a compressed frame including a skipped macro block. The processor implements the method, and the computer readable medium contains processor instructions.

FIELD OF THE INVENTION

The present invention relates to video compression and, in particular,to a system and method for enhancing compression using skip macro blockon a compressed video data stream.

BACKGROUND

The basic structure of advanced video compression standards may dividethe video frames into two main types of frames: independent frames, alsoknown as INTRA frames (or I-frames) and dependent frames, also known asINTER frames (or predicted (P) and/or bidirectionally predicted (B)frames).

INTER frames may be smaller than INTRA frames because they arecompressed with respect to other frames. INTER frames may be expressedin terms of or in relation to one or more neighboring frames, and maycontain only the difference between the current motion compensated frameand a reference frame.

Each INTER frame may be divided in to smaller segments, which are calledmacro blocks (MB). In the encoding process, the encoder may search forsimilar MBs in the reference frame. The spatial displacement between thelocation of the MB in the current frame and the location of the mostsimilar segment in the reference frame is called a motion vector (MV).Each encoded MB may be built out of two main parts: the MV, and thedifference from the reference segment.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIG. 1 schematically illustrates a system in accordance with anembodiment of the invention;

FIG. 2 illustrates a process in accordance with an embodiment of theinvention;

FIG. 3 illustrates a process in accordance with an embodiment of theinvention;

FIG. 4 illustrates a group of pictures in accordance with an embodimentof the invention;

FIGS. 5A-5B illustrate two frames from a group of pictures in accordancewith an embodiment of the invention;

FIGS. 6A-6C illustrate two frames having the same image content inaccordance with an embodiment of the invention;

FIGS. 7A-7B illustrate two frames having the same image content inaccordance with an embodiment of the invention;

FIG. 8 schematically illustrates a system in accordance with anembodiment of the invention; and

FIG. 9 schematically illustrates a system in accordance with anembodiment of the invention.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

DEFINITION OF TERMS

The terms used in this specification generally have their ordinarymeanings in the art, within the context of the invention, and in thespecific context where each term is used. Certain terms are discussedbelow, or elsewhere in the specification, to provide additional guidanceto the practitioner in describing the devices and methods in accordancewith embodiment(s) of the invention and how to make and use them. Itwill be appreciated that the same thing can be said in more than oneway.

Consequently, alternative language and synonyms may be used for any oneor more of the terms discussed herein, nor is any special significanceto be placed upon whether or not a term is elaborated or discussedherein. Synonyms for certain terms are provided. A recital of one ormore synonyms does not exclude the use of other synonyms. The use ofexamples anywhere in this specification, including examples of any termsdiscussed herein, is illustrative only, and in no way limits the scopeand meaning of the invention or of any exemplified term. Likewise, theinvention is not limited to the preferred embodiments.

“Playback device” means an appliance that is capable of receiving,rendering, and optionally transmitting audio, video, or audiovisualdata, including digital media.

“Image,” “video,” and the like, mean any information in any analog ordigital format (either in the compressed or expanded domain) which canbe displayed, rendered or perceived in sight and/or sound, with orwithout any other accompanying information that is “hidden,” i.e., notdisplayed, rendered or perceived. For example, motion action, stillaction, and/or a series, or sequences, of still action.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, and components have notbeen described in detail so as not to obscure the present invention.

A system and a method in accordance with embodiments of the inventionmay analyze a compressed video stream in real-time and may reduce thesize of the compressed video stream by replacing static and lowimportance blocks with a “skipped” marking in the compressed stream.This may result in storage and bandwidth savings with a substantiallyunnoticeable or negligible loss in video quality.

For example, video surveillance scenes may be static with a lowpercentage of moving objects. The higher the resolution, the higher thenumber of blocks that can be transformed to skipped blocks resulting ina reduced stream size. To avoid missing small changes betweenconsecutive frames, a method in accordance with an embodiment of theinvention may generate an interest bitmap, e.g., both spatially andtemporally, for a group of pictures (GOP). The method can be utilized ina video recorder, a network infrastructure, or on a capturing device, ata network video encoder or at an IP video camera.

In order to reduce the bit rate, an encoder may choose to discardinformation from static areas of the frame. The encoder may do this bymarking the MB as “skipped.” This decision may be based on a small orabout zero MV, e.g., less than a predetermined motion vector threshold,and a very small difference from the reference segment. In the skippedareas, the image may not change, thereby maintaining the informationfrom a previous frame. The distortion from skipping a MB can gounnoticed in static areas of the scene. A motion vector may show adisplacement within a MB between the current video frame and a referencevideo frame (either a previous or future frame). The resolution of themotion vector may be in quarter pixels. In one implementation the motionvector threshold may be about a half-pixel hypotenuse to distinguishbetween noise and actual motion (e.g., a motion vector threshold about0.5).

A real time encoder may determine whether to skip a MB based oninformation from at least two frames: the current frame and thereference frame. In the event the decision is wrong, the encoder mayhave to encode the accumulated difference in the next frame. An encodermay not use this option often and might refresh static background MBevery few frames.

A method in accordance with an embodiment of the invention may reducethe bit rate of compressed video in real time, by replacing an encodedMB with a skipped MB. The method can skip a MB based on an analysis ofthe MV and its difference from a reference segment over long periods oftime. The method may result in video data having an unnoticeablereduction in quality, which may be limited to areas of the scene with nomotion. Because the method may analyze and edit the video in thecompressed domain, it may use limited resources (e.g., time, memory,overhead, etc.).

FIG. 1 schematically illustrates system 10 in accordance with anembodiment of the invention. System 10 may be configured to captureimages, encode the images, and transmit a compressed video stream acrossa network to a recorder that may be configured to implement the skip MBmethod in accordance with an embodiment of the invention. The recordermay be configured to transmit the skipped MB compressed video across anetwork (either the same or different network) to an image playbackstation.

As shown in FIG. 1, the video images may be captured by image capturedevice 11. The image capture device may be analog camera 12 and/orInternet protocol (IP) camera 18. The analog signal from analog camera12 is provided to digitizer 14. The digitized video output of digitizer14 may be provided to encoder 16, which may be a network video encoder.IP camera 18 may include a network video encoder, which encodes thevideo internal to the IP camera. Encoder 16 and/or the internal encoderof IP camera 18 may be real time encoders and each may produce anencoded digital video image.

Encoder 16 and/or IP camera 18 may be in communication with networkdevice 20. Network device 20 may support an electronic communicationnetwork (e.g., Internet, local area network, wide area network, virtualprivate network, etc.). The encoded video from either encoder 16 or IPcamera 18 may be streamed via network 20 to recorder 30. The recordermay store the transmitted video from encoder 16 or IP camera 18 inmemory storage unit 34.

Recorder 30 may include skip MB processor 32 and may also include memorystorage unit 34. Skip MB processor 32 may perform the skip MB process inaccordance with an embodiment of the invention on the encoded digitalcompressed video. As mentioned above, the skip MB process may furtherreduce the size of the input compressed video. The skipped MB compressedvideo may be stored in memory storage unit 34. When a video is to beviewed, the recorder may extract the skip MB compressed encoded digitalimage from memory storage unit 34 and transmits the skip MB compressedencoded digital image via network device 22 to playback device 40.

In other implementations, skip MB processor 32 may be located at imagecapture device 11A (FIG. 8). In this implementation, the streamingbetween the recorder and the input devices may require significantlylower bandwidth. In an alternative implementation, skip MB processor 32may be located at network device 20A (FIG. 9). In this implementation,the streaming to the recorder may require significantly lower bandwidth.

In other implementations, memory storage unit 34 may be remotely locatedfrom, and in electronic communication with, recorder 30. The recordedneed not be the only device in system 10 that can access the videostored within memory storage unit 34. For example, playback device 40may be in electronic communication with the memory storage unit vianetwork 22. Although FIG. 1 depicts network device 20 and network device22 as different network devices, in one implementation there may be onenetwork device supporting one electronic communication networkinterconnecting the image capture device, recorder, playback device, andmemory storage units.

Playback device 40 may include decoder 42, player 44, and monitor 46.Decoder 46 decodes the compressed encoded digital image stream providedvia network 22. Player 44 may playback the decoded video stream and mayprovide the video to monitor 46 so that it may be viewed by a user.

The skip MB process in accordance with an embodiment of the inventionmay maintain the compatibility of the skipped MB compressed stream to avideo standard, and can be applied to video standards such as MPEG2,MPEG4, H.264, etc.

The skip MB process in accordance with an embodiment of the presentinvention may be an internal process in recorder 30, which may performthe skip MB compression before the video stream is stored in memorystorage unit 34. A macro block may be the smallest element in thecompressed video's bit stream that has a header. The number of blocks ina MB may vary based on the video content and the compression standardapplied by the encoder located upstream to recorder 30. The skip MBprocess in accordance with an embodiment of the present invention maydecide which MB to keep and which MB to skip or delete from the stream.

FIG. 2 illustrates process 200 that produces a compressed video streamin accordance with an embodiment of the invention. Process 200 may beperformed by recorder 30; in particular by skip MB processor 32. A codedvideo sequence may be provided as input, step 210, to the recorder. Thisinput may be a compressed video stream done in accordance with a videostandard. A decision may be made as to whether a frame is an INTERframe, step 220. If the frame is not an INTER frame, the frame may becombined, step 260, to the bit stream output. The bit stream output maybe saved, step 270, as part of the skipped MB compressed video stream.

If the frame is an INTER frame, then process 200 may continue at step230. At step 230, entropy decoding may be performed on the INTER frame.The entropy decoding process may be implemented in hardware, software,or a combination of hardware and software. Entropy decoding may includevariable length decoding, binary arithmetic decoding, etc. and may beperformed to reverse the entropy encoding (e.g., variable length coding,binary arithmetic encoding, etc.) done when the video was encoded. Theentropy decoding process may reveal the motion vector and may alsoreveal the size of each macro block.

After the INTER frame has been decoded, the frame may undergo INTERcompression, step 240. INTER compression is described below withreference to FIG. 3.

After INTER compression has been performed on the INTER frame, entropyencoding may be performed, step 250, on the INTER frame. Theentropy-encoded INTER frame may then be combined, step 260, with theuntouched INTRA frames into a bit stream output. The bit stream outputmay be saved in a storage medium, step 270, as part of the skipped MBcompressed video stream.

FIG. 3 illustrates process 300 in accordance with an embodiment of theinvention. Process 300, which may be performed by recorder 30 and moreparticularly skip MB processor 32, performs INTER compression (FIG. 2,step 240) on the decoded INTER frame. Process 300 may begin the INTERcompression process by receiving, step 310, an INTER frame MB afterundergoing entropy decoding.

All the MB within a group of pictures (GOP) may be saved, step 320, in amemory unit accessible by the skip MB processor. Because a skip MBprocess in accordance with an embodiment of the invention may be done onan INTER frame, any INTRA MB within the decoded INTER frame may beseparated, step 330.

The INTRA MB may exist in one or more INTER frames to track highdifferences compared to a previous frame and/or to avoid the extraoverhead of INTRA frames by embedding an INTRA MB within an INTER frame.This process may require reading the MB header in order to resolve itstype. An INTRA macro block is an anchor MB, and may be defined as thosemacro blocks in an INTER frame that are fully-specified—e.g., notdefined with reference to another frame. Those MBs that are INTRA MBsmay be saved, step 385, and then may be merged with any skipped MBs toform a new compressed frame, step 390.

FIG. 4 illustrates GOP 400 in accordance with an embodiment of theinvention. GOP 400 may include frames 410-418. Within frames 410-418 maybe MBs 420-428. MBs 420-428 each may have positional correspondence toone another, in that they may each be located in the same motioncompensated location within their respective frame (i.e., relativespatial position to a previous and/or a future frame). Frame 410 mayinclude a MB 420 that may be an area-of-interest having motion. Thearea-of-interest of MB 420 may affect other positional corresponding MBs422-428 in frames 412-418. The MB bitmaps for frames 422-428 may createa uniform area-of interest for all the frames in the GOP. Accordingly,in accordance with an embodiment of the invention, all the coded MBs422-428 may be saved in frames 410-418 and not skipped during INTERcompression process 300.

A GOP may be a sequence of frames between two consecutive INTRA frames.Process 300 may be applied to a full GOP. For example, if a MB in theGOP is a MB with motion, all the positional corresponding MBs in therest of the frames within the same GOP may also be considered to havemotion.

FIGS. 5A-5B illustrate frames 510, 512 from a group of pictures inaccordance with an embodiment of the invention. Within frame 510 may bean area-of-interest 520 having two objects moving inside thearea-of-interest—i.e., two individuals approaching along the samecorridor. Frame 512 may depict the same, or similar, area-of-interest520 where the two objects' positions have moved within thearea-of-interest—i.e., the two individuals have gotten closer in thecorridor.

With reference again to FIG. 3, a determination may be made, step 340,as to whether an INTER MB under consideration has motion. If there ismotion, the INTER MB may be saved, step 385, and then may be merged withany skipped MB frames to form a new stream, step 390.

A MB may be treated as a MB with motion if the MB has a MV greater thana predetermined threshold, or if the MB is coded as an INTRA MB. Inaccordance with an embodiment of the invention, the MV predeterminedthreshold may be about zero.

If there is no motion within the INTER MB, process 300 continues to step350 where a decision is made as to whether the INTER MB underconsideration is near a MB with motion (e.g., a MB to the right, left,up, and/or down or diagonally (upper-right, upper-left, lower-right,lower-left) in a motion bit-map that may be generated per GOP). If so,the INTER MB may be saved, step 385, and then may be merged with anyskipped MBs to form a new compressed frame, step 390.

After step 350, process 300 may continue at step 360, where adetermination may be made as to whether the INTER MB under considerationis large. A large-sized MB may be treated as an MB with motion. A MB maybe considered to be a large-sized MB if it is greater than apredetermined MB bit size threshold.

The MB bit size is a compression result and may be related to thedifference of a MB compared to a MB from a previous frame in combinationwith a motion estimation performed by the encoder. For example, if thereis no MV compared to a previous MB there may still be a difference inpixel values which may be encoded. If the size (in bits) of theresultant MB is not greater than a predetermined threshold, the MB maybe potentially skipped. In one embodiment in accordance with theinvention, the MB bit size threshold may be about 0 bits, about 100bits, about 400 bits, about 500 bits, or about 1,000 bits. The MB bitsize threshold may be representative of the skip MB compression strength(e.g., a zero threshold may mean no skip MB compression, and a thresholdof 500 may mean a stronger skip MB compression strength). If the MB sizeis greater than the predetermined MB size threshold, the INTER MB may besaved, step 385, and then may be merged with any skipped MBs to form anew compressed frame, step 390.

FIGS. 6A-6C illustrate frames 600, 600′, 600″, where each of frame 600,600′, 600′ is the same image but produced using different sizethresholds in step 360 in accordance with an embodiment of theinvention. Marked areas 610 in FIGS. 6A-6C are coded MB (e.g., notskipped MBs) while the unmarked areas are skipped MB. For instance, theareas around the counter where the desk clerk and patron appear are notskipped MB, while the floor and walls in other portions of frames 600,600′, 600″ are skipped MB. By increasing the MB size threshold, more ofimages 600, 600′, and 600″ may undergo the skip MB process in accordancewith an embodiment of the invention. Because the large-sized MBs are notprocessed, the overall image is not impacted.

With reference again to FIG. 3, process 300 may continue at step 370,where a determination may be made as to whether the current INTER MBunder consideration follows a previous GOP with motion in a positionalcorresponding MB. If a positional corresponding MB was treated as a MBwith motion in previous GOPs it may also be treated as a MB with motionin the current GOP. By applying this criterion, small moving objects inan area-of-interest may be kept in the image, even in a GOP where thesmall object's motion was too little to create a MV. The number of GOPsfor which the skip MB process in accordance with an embodiment of theinvention may “save” a motion may be a predetermined parameter providedto the process.

If the INTER MB under consideration follows a previous GOP with motionin its MB, the INTER MB may be saved, step 385, and then may be mergedwith any skipped MBs to form a new compressed frame, step 390.

In one implementation, the INTER MB under consideration may be saved ifit has positional correspondence with a MB in a previous GOP whichsatisfies at least one of the conditions of steps 340, 350, and 360.

A morphological dilation operation may also be applied to extend an areamarked as including motion. A dilation operation may use a structuringelement for probing and expanding the shapes contained in the inputimage. FIGS. 7A-7B illustrate frame 700, 700′, where the same image isdisplayed, but produced without (FIG. 7A) and with (FIG. 7B)morphological dilation. As shown in FIG. 7A, area-of-interest 710 (e.g.,the area marked as including motion) without the dilation may not be ascomplete as the area-of-interest 710′ shown in FIG. 7B. Because therewas no morphological dilation operation, area-of-interest 710 may failto include part of the moving objects.

With reference to FIG. 3, at step 380, the INTER MB under considerationmay be deleted and marked as skipped in the bit stream. A new stream maybe assembled, step 390, from any INTRA MBs and INTER MBs that may havebeen saved at step 385. This new compressed frame may be provided toprocess 200 to undergo entropy encoding, step 250 (FIG. 2), as describedabove.

The skip MB process in accordance with an embodiment of the inventionmay be a low resources process that could reduce storage requirement fora large facility with multiple surveillance cameras. The storagereduction percentage may be a factor of the compression standard, theGOP size, the content of the video scene, and the bit rate and/or theresolution of the entropy encoding stage. The process may have low CPUusage because it works on the frames in their compressed form.

Tables I and II illustrate the saving percentage measured for a varietyof commercially available surveillance IP camera systems after theirvideo streams for a variety of images underwent the skip MB process inaccordance with an embodiment of the invention. As shown in Tables I andII, a reduction in storage requirement of up to 50% may be achieved.

TABLE I NICE Image: Parking1 Yard Parking2 Casino Vendor/model: ArecontPanasonic AXIS NICE 2105 502 Q7401 NVE1008 Resolution: 2 MP 1 MP 4 CIF 4CIF Saving (percent): 42% 25% 9% 12%

TABLE II Parking NICE Image: Junction Avenue night Yard CorridorVendor/model: NICE Arecont NICE AXIS NICE NVE1008 2105 NVE1008 P3301NVE1008 Resolution: CIF 2 MP CIF VGA 4 CIF Saving (percent) 8% 50% 16%26% 40%

In accordance with an embodiment of the invention, a computer programapplication stored in non-volatile memory, or computer-readable medium(e.g., register memory, processor cache, RAM, ROM, hard drive, flashmemory, CD ROM, magnetic media, etc.) may include code or executableinstructions that when executed may instruct or cause a controller orprocessor to perform methods discussed herein such as a method for realtime bit rate reduction in compressed video streams.

The non-volatile memory and/or computer-readable medium may be anon-transitory computer-readable medium including all forms and types ofmemory and all computer-readable media except for a transitory,propagating signal.

While there have been shown and described fundamental novel features ofthe invention as applied to several embodiments, it will be understoodthat various omissions, substitutions, and changes in the form, detail,and operation of the illustrated embodiments may be made by thoseskilled in the art without departing from the spirit and scope of theinvention. Substitutions of elements from one embodiment to another arealso fully intended and contemplated. The invention is defined solelywith regard to the claims appended hereto, and equivalents of therecitations therein.

We claim:
 1. An apparatus for further compressing a compressed videohaving a plurality of groups of pictures, each group of picturesincluding at least one INTRA frame and a plurality of INTER frames, theapparatus comprising: a memory; and a processor configured to: receivethe compressed video stream; for each INTER frame: perform entropydecoding to reveal motion vectors and bit sizes of encoded macro blocksfrom the compressed video stream; perform a skip macro block compressionbased on the motion vectors and on the bit sizes of macro blocks,wherein the skip macro block compression comprises deleting, from thecompressed video stream, an encoded macro block and replacing theencoded macro block with a macro block marked as skipped if thefollowing conditions are met: the encoded macro block is an INTER macroblock; the encoded macro block has a motion vector less than apredetermined threshold; the encoded macro block is not near a macroblock with motion; the encoded macro block bit size is less than apredetermined macro block size threshold; and macro blocks in one ormore frames of previous groups of pictures, that have a positionalcorrespondence with the encoded macro block, have no motion; performentropy encoding on the INTER frame; and combine the INTER frame to anoutput bit stream.
 2. The apparatus of claim 1, the processor furtherconfigured to place the compressed frame in a position within the groupof pictures corresponding to an original position of the at least oneINTER frame.
 3. The apparatus of claim 1, wherein the processor isconfigured to save an INTRA macro block to the output bit stream.
 4. Theapparatus of claim 1, the processor further configured to apply amorphological dilation operation to extend an area marked as includingmotion within the INTER frame.
 5. The apparatus of claim 1, wherein theprocessor is located in one of an image capture device, a networkdevice, and a recorder.
 6. A method for of further compressing acompressed video having a plurality of groups of pictures, each group ofpictures including at least one INTRA frame and a plurality of INTERframes, the method comprising: receiving the compressed video stream;for each INTER frame: performing entropy decoding to reveal motionvectors and bit sizes of encoded macro blocks from the compressed videostream; performing a skip macro block compression based on the motionvectors and on the bit sizes of macro blocks, wherein the skip macroblock compression comprises deleting, from the compressed video stream,an encoded macro block and replacing the encoded macro block with amacro block marked as skipped if the following conditions are met: theencoded macro block is an INTER macro block; the encoded macro block hasa motion vector less than a predetermined threshold; the encoded macroblock is not near a macro block with motion; the encoded macro block bitsize is less than a predetermined macro block size threshold; and macroblocks in one or more frames of previous groups of pictures, that have apositional correspondence with the encoded macro block, have no motion;performing entropy encoding on the INTER frame; and combining the INTERframe to an output bit stream.
 7. The method of claim 6, furthercomprising saving an INTRA macro block to the output bit stream.
 8. Themethod of claim 6, wherein the predetermined macro block size thresholdis one of 0 bits, 100 bits, 400 bits, and 500 bits.
 9. The method ofclaim 6, wherein the predetermined motion vector threshold is one of 0pixels and 0.5 pixel.
 10. The method of claim 6, further includingapplying a morphological dilation operation to extend an area marked asincluding motion in the INTER frame.
 11. A non-transitory computerreadable medium having stored thereon instructions which when executedby a processor cause the processor to perform the method of furthercompressing a compressed video having a plurality of groups of pictures,each group of pictures including at least one INTRA frame and aplurality of INTER frames, the method comprising: receiving thecompressed video stream; for each INTER frame: performing entropydecoding to reveal motion vectors and bit sizes of encoded macro blocksfrom the compressed video stream; performing a skip macro blockcompression based on the motion vectors and on the bit sizes of macroblocks, wherein the skip macro block compression comprises deleting,from the compressed video stream, an encoded macro block and replacingthe encoded macro block with a macro block marked as skipped if thefollowing conditions are met: the encoded macro block is an INTER macroblock; the encoded macro block has a motion vector less than apredetermined threshold; the encoded macro block is not near a macroblock with motion; the encoded macro block bit size is less than apredetermined macro block size threshold; and macro blocks in one ormore frames of previous groups of pictures, that have a positionalcorrespondence with the encoded macro block, have no motion; performingentropy encoding on the INTER frame; and combining the INTER frame to anoutput bit stream.
 12. The non-transitory computer readable medium ofclaim 11, the instructions including: saving an INTRA macro block. 13.The non-transitory computer readable medium of claim 11, theinstructions including: wherein the predetermined macro block sizethreshold is one of 0 bits, 100 bits, 400 bits, and 500 bits.
 14. Thenon-transitory computer readable medium of claim 11, the instructionsincluding: wherein the predetermined motion vector threshold is one of 0pixels and 0.5 pixel.
 15. The non-transitory computer readable medium ofclaim 11, the instructions including: applying a morphological dilationoperation to extend an area marked as motion in the INTER frame.